Electronic Differential Control of Rear-Wheel Independent-Drive Electric Vehicle

To track desired slip ratios and desired longitudinal speeds at the centers of driving wheels in the curve, this article proposes a hierarchical structured electronic differential control (EDC) of rear-wheel independent-drive electric vehicle (EV). In the high-level control, a fuzzy algorithm-based coefficient is computed according to the driver's emotional intention of acceleration. The fuzzy algorithm-based coefficient is used to correct the desired driving torque of vehicle transmitting to the medium-level control. In the medium-level control, an optimization algorithm is developed to allocate the desired torques with requirement of as much accurate yaw moment as possible by the desired driving torque of the vehicle and yaw moment. And the desired longitudinal speeds at the centers of the rear left and right wheels are corrected twice, respectively, by Ackermann steering principle, considering the slip angle of the wheel and yaw moment. Based on the desired torques and desired longitudinal speeds at the centers of the rear left and right wheels from the medium-level control, desired slip ratios and desired angular speeds of the rear left and right wheels which are control signals for in-wheel-motor controllers are computed sequentially by adopting an inverse model of the Magic Formula. The square root of the sum of squares (SRSS) of tracking errors of the rear left and right wheel is adopted as the tracking error index of longitudinal speeds at the centers and slip ratios of the rear left and right wheels. In steering maneuvers of step steering and double lane change, simulation results based on MATLAB/Simulink indicate that the proposed EDC can improve tracking accuracy of longitudinal speeds at the centers and slip ratios of the rear left and right wheels compared with two EDCs for comparison. The two EDCs are an EDC based on Ackermann steering principle and an EDC based on the proposed EDC with the simplified desired longitudinal speed at the center of the wheel. The proposed EDC has better performance in tracking road trajectory, the desired vehicle longitudinal velocity and desired yaw rate compared. Finally, the robustness of the proposed EDC is verified under the slalom test.